Major effort continues to be given to understanding aspects of photon migration in turbid biological media. Emphasis is on analyzing photon propagation through layered biological structures. Results can be applied to various non-invasive medical diagnostic procedures which involve the scattering and absorption of laser light in situ, on example being the measurement of hemoglobin oxygenation in the brain by time-resolved absorption spectroscopy. In the latter instance, passage of near-infrared radiation through the head has been modelled by a composite structure consisting of a layer of optically dense material (the skull) overlying a region of lower scattering density but higher absorption (blood-containing tissue), and mathematical expressions have been derived for several parameters pertaining to the time course of photon reemission.